Thursday, November 01, 2012

Winter Forecast 2012-13: Nino Or Not

We were trending towards a Nino earlier in the summer but such a trend is not reality at this point.  Subsurface cooling in the Eastern Pacific nudged to the surface and an earlier trend towards Nino is now a trend towards "neutral" conditions in the Pacific.   There are pockets of warm water out there -- especially to the south of Central America and farther west towards the International Date Line.  However, the Pacific has a colder than average look to it at this point.

You can see that subsurface cooling I was talking about in the chart up above -- this shows the temperature anomaly below the surface across the Pacific along the equator.  Cooler water below the surface nudged upwards and mitigated the warming trend that had taken place earlier this summer.  The result was an abrupt stop to the warming in the Eastern Pacific and a neutral hold in the pattern.  However, as we moved into October that cooling is easing and we're starting to see some warmer anomalies develop below the surface.  Whether those continue to warm or not remain to be seen but it does appear the cooling is stopping and perhaps will reverse into November.
The idea of a major warmup in Nino into the winter is one that most modeling does not hold onto.  Most models suggest a neutral to warmish neutral ENSO state for the coming winter.  This means an ENSO state not like 2009-2010 or like 2002-2003..but perhaps one that is more like 2003-2004...or perhaps 1992-1993...or perhaps 2006-2007.

2003-2004 was a colder than average winter for us with around normal snowfall. 1992-93 brought us the superstorm. Both winters were ENSO positive but were not "true" Nino winters, meaning that the eastern Pacific was warmer than average but not warm enough to be classified as a true El Nino.  2006-2007 is a bit closer to a Nino than neutral and average comes in really close according to MEI.  That winter was known for volatility, swinging from 70's in golfing in early January to scraping out sleet in February and March.

Using the MEI (an ENSO index) as my that I love to use in winter forecasting although it's not perfect, there are seven years where the MEI ranged between .3 and .7 in the July/August and August/September data set.  Of those seven, six had a positive ENSO state into the following winter:

1953...barely for the winter (DJF average was 0.081)

The one other year that matches the data set, 1980, ended up ENSO negative in the winter of 80-81 by a smidge so it gets thrown out as criteria for this data set is ENSO+ for December through February.

How did these winters stack up?

Winter results at PHL (temps, snowfall)
53-54: 37.4, 22.6"
58-59: 31.4, 5.1"
63-64: 30.9, 32.9"
92-93: 36.3, 24.3"
03-04: 32.8, 18.0"
04-05: 35.2, 30.4"
Average: 34.0, 20.6"
Current Norm:  35.3, 21.8"

There are several ENSO positive but not Nino winters going back through the years -- they are very much mixed bag in nature and range from cold to warm, stormy to not. The 58-59 winter was one of the driest locally on record and didn't produce much snow despite being quite cold. Each of the years in the above data set are mixed bag but aren't terribly far from average on other side of the fence except the dry winter of 1958-59.  If we don't see a nudging in ENSO state to a weaker Nino, the drivers for this winter will be less on the Pacific side of the fence and more based on what goes on in the higher latitudes in the Arctic, Atlantic, Pacific, and Russia.